Metal Polishing Advice

[Jordan]

I was shown how to strip chrome and nickel at a trade training college. They had a vented hood over the dechroming and denickeling baths to control noxious fumes, but I guess if you did it outdoors it'd be safe enough. Looking for my notes, I came across something posted by a Ducati restorer. I hope he doesn't mind it repeated here.

" Stripping
by John Withers

TO STRIP CHROMIUM DEPOSITS - Firstly you will need a plastic bucket, small tin of Caustic Soda, 6 Volt bike or car Battery, and a small bit of steel sheet about 3in square. (Set up as per diagram A) Method: Fill bucket with water then slowly add the caustic soda, this process generates a lot of heat so take it easy, next suspend the steel plate in the solution with a bit of steel wire and connect it to the negative terminal of the battery, you can now place the item to be stripped in the bucket, being careful not to touch the negative
steel plate, now connect the battery positive to item using steel or copper wire, gas will be seen coming from the steel plate which indicates that the stripping action has commenced. Slowly the chrome will start to disappear from the item, which will then gas freely once all the chrome has been removed, if stripping hard chrome deposits be prepared for a fairly long time in stripping, however if stripping decorative chrome it will take only a few seconds, leaving the bright nickel exposed (yellow in colour as opposed to chrome blue). All stripping action will cease once the chrome has been removed. If desired nickel can be polished to a high finish at this stage. (see polishing article next month)

TO STRIP NICKEL DEPOSITS - This is only necessary if the surface of the nickel is broken up by damage or rust etc. You will need a quantity of weak Sulphuric Acid or old Battery Acid, a plastic container, (size dependant on how much acid you have, or size of job to be stripped) a 6 Volt Battery, and a 3in square section of Lead sheet (As per diagram B). Method: Immerse the lead sheet in the acid, using lead strips to electrically connect to the negative terminal of the battery. Suspend job to be stripped by copper wire and place in the solution making sure the job does not touch the negative plate, connect to the battery positive. This process take a little longer than chrome stripping due to the generally thicker deposit, keep an eye on the job as the stripping proceeds, as unlike the chrome stripping solution the nickel strip will carry on long after the nickel has gone and deeply etch into the base metal, ruining the part if you forget to remove it when the stripping is completed.

TO STRIP ZINC AND CADMIUM - You will require a plastic container, and a quantity of Hydrochoric Acid (Spirit of Salt) this is obtainable from your local hardware store and is sold for the purpose of cleaning bricks. Method : This process is purely a chemical one so a battery is not needed, simply immerse parts to be stripped in the solution, gassing will start almost immediately and stop when all traces of cadmium or zinc are removed. This solution will also remove light surface rust fairly quickly when it is warm ie, during summer. After extended use, it will become very slow and then stop, do not throw away as it is now called "Killed Spirit" and is one of the best soldering fluxes around.

TO STRIP COPPER - You will require a Plastic Container and a quantity of Ferric Chloride which is obtainable from any electronic hobby shop, Dick Smith etc, it is used for producing printed CCT boards, etching away the copper after CCT has been printed or drawn. Ferric Chloride comes either in solution or as crystals, if you obtain the crystals they will have to be diluted with water before use. On some of the decorative chrome items you have already stripped of nickel and chrome, you will find a layer of copper underneath, electroplaters use this copper layer to cut down on the labour involved in polishing steel base metals, as copper is relatively soft and takes a most brilliant polish. It does not however improve corrosion resistance as it is most commonly thought, quite the opposite is true due to electrolytic interaction between the differing layers of metals. Method: Warm solution by immersing plastic container in a larger container containing hot water, place part in solution until copper is removed. As in zinc and cadmium stripping no electrical current is required with this method. Remember it is not always necessary to strip copper, as stated previously It takes a brilliant polish, stripping will only be necessary when the plate is badly corroded or damaged.

It should be remembered that rubber gloves and eye protection should be used during all stripping processes, and always keep a bucket of water handy for swilling purposes.

Okay, now you have all those de-rusted, and de-plated items ready. Items to be sent for cadmium or zinc can be sent directly to the platers although burred nuts etc can be dressed up with a file, electroplating does not repair items! Next month I will cover the methods for those items that require polishing, and the materials you will need.
"

[Pete]

Just as a warning, if you use ferric chloride to etch away copper, be aware that it will also etch the base steel part. So much so, that if you were to leave it in the bath long enough, the part would be gone. ( it will take a days to completely dissolve the part ) You have to watch for the color change to know when the copper is all gone. Some thing like ammonium persulfate will etch the copper without etching the steel, but it is a little more caustic to your skin.

Pete

[spaynenda]

Okay, so here are the results. I told the polisher to do a "mirror polish" on the fork shrouds, because the one was so badly gouged, I was worried anything less would not do the job. Amazingly, they both turned out great, so looks like I don't need to send away to Oz for a replacement.

Everything else I had brought to "original" condition, what they call "pre-pl." Some of the flaws didn't come out, but there's a nice patina that I'm really pleased with on the hubs, triple clamp and headlight brackets. The bike won't win any contests, but I think it'll be just the look I want.

Thanks for all the advice.

Sheldon